001    /*
002     * Copyright (C) 2012 eXo Platform SAS.
003     *
004     * This is free software; you can redistribute it and/or modify it
005     * under the terms of the GNU Lesser General Public License as
006     * published by the Free Software Foundation; either version 2.1 of
007     * the License, or (at your option) any later version.
008     *
009     * This software is distributed in the hope that it will be useful,
010     * but WITHOUT ANY WARRANTY; without even the implied warranty of
011     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
012     * Lesser General Public License for more details.
013     *
014     * You should have received a copy of the GNU Lesser General Public
015     * License along with this software; if not, write to the Free
016     * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
017     * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
018     */
019    
020    package org.crsh.util;
021    
022    import java.io.Serializable;
023    
024    /**
025     * An immutable sequence of white spaces.
026     */
027    public class BlankSequence implements CharSequence, Serializable {
028    
029      /** . */
030      private static final BlankSequence[] CACHE = new BlankSequence[64];
031    
032      static {
033        for (int i = 0;i < CACHE.length;i++) {
034          CACHE[i] = new BlankSequence(i);
035        }
036      }
037    
038      public static BlankSequence create(int length) {
039        if (length < 0) {
040          throw new IllegalArgumentException("No negative length accepted");
041        }
042        if (length < CACHE.length) {
043          return CACHE[length];
044        } else {
045          return new BlankSequence(length);
046        }
047      }
048    
049      /** . */
050      private final int length;
051    
052      /** . */
053      private String value;
054    
055      /**
056       * Build a new blank sequence.
057       *
058       * @param length the length
059       * @throws IllegalArgumentException when length is negative
060       */
061      private BlankSequence(int length) throws IllegalArgumentException {
062        if (length < 0) {
063          throw new IllegalArgumentException();
064        }
065    
066        //
067        this.length = length;
068        this.value = null;
069      }
070    
071      public int length() {
072        return length;
073      }
074    
075      public char charAt(int index) {
076        checkIndex("index", index);
077        return ' ';
078      }
079    
080      public CharSequence subSequence(int start, int end) {
081        checkIndex("start", start);
082        checkIndex("end", end);
083        if (start > end) {
084          throw new IndexOutOfBoundsException("Start " + start + " cannot greater than end " + end);
085        }
086        return new BlankSequence(end - start);
087      }
088    
089      @Override
090      public String toString() {
091        if (value == null) {
092          if (length == 0) {
093            value = "";
094          } else {
095            char[] chars = new char[length];
096            for (int i = 0;i < length;i++) {
097              chars[i] = ' ';
098            }
099            value = new String(chars, 0, chars.length);
100          }
101        }
102        return value;
103      }
104    
105      private void checkIndex(String name, int index) {
106        if (index < 0) {
107          throw new IndexOutOfBoundsException("No negative " + name + " value " + index);
108        }
109        if (index > length) {
110          throw new IndexOutOfBoundsException("The " + name + " value " + index + " cannot greater than length " + length);
111        }
112      }
113    }